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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Photofragment Translational Spectroscopy Studies of H Atom Loss Following Ultraviolet Photoexcitation of Methimazole in the Gas Phase
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Photofragment Translational Spectroscopy Studies of H Atom Loss Following Ultraviolet Photoexcitation of Methimazole in the Gas Phase

机译：气相中甲基唑紫外线磷酸含量损失H原子损失的光折叠平移光谱研究

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摘要

The ultraviolet (UV) photodissociation of gas-phase methimazole has been investigated by H Rydberg atom photofragment translational spectroscopy methods at many wavelengths in the range of 222.5-275 nm and by complementary electronic structure calculations. Methimazole is shown to exist predominantly as the thione tautomer, 1-methyl-2(3H)-imidazolinethione, rather than the commonly given thiol form, 2-mercapto-1-methylimidazole. The UV absorption spectrum of methimazole is dominated by the S-4 - S-0 transition of the thione tautomer, which involves electron promotion from an a' (p(y)) orbital localized on the sulfur atom to a sigma* orbital localized around the N-H bond. Two H atom formation pathways are identified following UV photoexcitation. One, involving prompt, excited-state N-H bond fission, yields vibrationally cold but rotationally excited methimazolyl (Myl) radicals in their first excited (A) over tilde electronic state. The second yields H atoms with an isotropic recoil velocity distribution peaking at low kinetic energies but extending to the energetic limit allowed by energy conservation given a ground-state dissociation energy D-0(Myl-H) similar to 24 000 cm(-1). These latter H atoms are attributed to the unimolecular decay of highly vibrationally excited S-0 parent molecules. The companion electronic structure calculations provide rationales for both fragmentation pathways and the accompanying product energy disposals and highlight similarities and differences between the UV photochemistry of methimazole and that of other azoles (e.g., imidazole) and with molecules like thiourea and thiouracil that contain similar N-C=S motifs.
机译：通过H rydberg原子的光代原料翻译光谱方法研究了气相甲基咪唑的紫外（UV）光解，在222.5-275nm的范围内，通过互补的电子结构计算。显示甲巯咪唑主要作为Thione互变异构体，1-甲基-2（3H） - 咪唑啉乙基，而不是通常给定的硫醇形式，2-巯基-1-甲基咪唑。甲基唑的UV吸收光谱由Thione互变异构体的S-4和S-0转变为主，这涉及从A'（P（Y））轨道局部化的电子促进到Sigma *轨道围绕NH债券定位。紫外线光透镜后鉴定了两种H原子形成途径。一种，涉及提示，激发态N-H粘结裂变，在其首次激发（A）上的Tilde电子状态下产生振动冷但旋转激发的甲基唑基（MyL）。第二次产生H原子，其具有在低动力学能量下达到峰值的各向同性的反冲速度分布，但是给出了相似的地面解离能量D-0（MyL-H）延伸到能量守恒允许的能量极限（MyL-H），其类似于24 000cm（-1） 。这些后者H原子归因于高度振动激发的S-0父母分子的单分子衰减。伴侣电子结构计算为碎片途径和随附的产品能量处理提供了理由，并突出了甲基唑的UV光化学之间的相似性和差异，以及含有硫脲和含有类似NC =的硫脲的分子等分子。 S主题。

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